This invention relates to a power driven rotary device, and particularly relates to a power driven rotary tool with spindle lock, brake and drag systems.
Power driven rotary devices drive a variety of different tools or bits for performing various work-related operations on a workpiece. For example, such devices are used to drill a hole, driving a threaded member, form and shape portions of a workpiece, and the like. Typically, a power-operated rotary tool or device includes a power driver and transmission, a spindle rotated by the power driver, and a bit-holder, such as a chuck, mounted onto a forward end of the spindle. When the tool is to be used, a tool bit, such as a drill bit, is mounted in the chuck with a working end of the tool bit extending outward from the chuck at a working end of the tool. The spindle, the chuck and the drill bit are rotated by the power driver, while the working end of the drill bit is being urged into the workpiece.
The chuck may include several clamping jaws which are radially and axially movable along paths within the chuck to converge clamping surfaces of the jaws into a clamping position about portions of a shank of the drill bit which has been positioned in axial alignment within the chuck.
In one type of chuck, referred to as a keyless chuck, an outer ring of the chuck can be rotated by the user to move the jaws and thereby clamp, or unclamp, the drill bit relative to the chuck. In using a keyless chuck, the main body of the chuck must be prevented from rotating while the ring is rotated by the user to effect the desired operation of the jaws. With the chuck mounted to the spindle of the tool, any attempt to rotate the ring of the chuck while holding the chuck body to prevent rotation of the body is a difficult task.
To assist the user of the tool in rotating the ring of a keyless chuck, while precluding any rotation of the chuck body, an automatic spindle lock was developed many years ago, an example of which is described and illustrated in U.S. Pat. No. 3,243,023, which issued on Mar. 29, 1966.
The automatic spindle lock includes several wedging rollers which are contained within a housing of the tool to facilitate the locking of the spindle, and thereby the chuck body, to the housing at any time when operating power is not being applied to the tool. This will assist the operator in adjusting the jaws of the chuck in the process of clamping, or unclamping, any bit with respect to the chuck.
The wedging rollers are each formed with an axis which, desirably, should be parallel with an axis of the spindle, and is spaced from the other rollers in a circular path about the spindle axis. Each of the rollers is located within a respective chamber which allows the rollers to be moved desirably laterally of the axis thereof within the circular path, resulting in a slight lost motion between the rollers and the spindle. Also, the rollers are allowed to move in a radial direction relative to the spindle axis, while desirably maintaining the parallel relationship with the spindle axis. Each chamber includes interfacing, radially spaced boundaries formed by a radially outboard fixed surface which is associated with the housing, and by an inboard surface which is associated with the spindle.
The rollers are mounted for passive movement in the circular path when power is being applied to the tool to rotate the spindle and the chuck in a rotational mode. When power is not being applied to the tool, the spindle and the chuck are not rotating and are in a non-rotational mode.
If, during the non-rotational mode, the operator desires to clamp, or unclamp, the bit with respect to the chuck, the operator holds the housing with one hand, and slightly turns the chuck in either direction whereby the rollers become wedged between the fixed surface of the housing and the inboard surface of the spindle to effectively and automatically lock the spindle and the chuck with the housing. While continuing to hold the housing with the one hand, the operator turns the ring on the keyless chuck to facilitate clamping, or unclamping, movement of the jaws thereof, to allow the bit to be retained with, or be removable from, the chuck.
While it is desirable that the axes of the rollers be maintained in parallel with the spindle axis as noted above, the rollers are occasionally skewed from the axial alignment due to the limited freedom of movement of the rollers within their respective chambers. Consequently, some portions of the skewed rollers may not be not fully wedged in place when the operator adjusts the chuck to effect the automatic locking of the spindle with the housing, thereby lowering the integrity of such automatic locking.
In view of this deficiency, there is a need for a facility for insuring that, in the automatic locking of the spindle to the housing, each roller is wedged fully in place, with the axis thereof being in parallel with the spindle axis, to obtain the maximum automatic locking possible.
When the tool is in operation, and the operating power is removed therefrom, the power driver begins to coast to a stop and, after a brief down-coasting period, eventually ceases to rotate. Due to the built-in lost motion noted above, the spindle tends to continue to rotate for a brief period at or near the normal operational speed, which is faster than the down-coasting speed of the power driver.
During the brief down-coasting period, the faster spindle moves slightly ahead of the slowing power driver to the extent that the wedging rollers become wedged whereafter a reactive force, resulting from an impact engagement of the faster spindle and the slowing power driver, causes the rollers to become unwedged. This condition can occur several times during the down-coasting period where the rollers may skew as noted above, and where the facing portions of the power driver, spindle and rollers repeatedly and engagingly interact to develop an undesirable chattering noise.
Therefore, there is a further need for a facility for reducing or eliminating the conditions which lead to the undesirable chattering noise, to thereby reduce or eliminate such noise.